1. Field of the Invention
The present invention generally relates to the development of distributed applications (for example, a computer teleconferencing system, on a remote desktop presentation system) and to the mechanism for using stand-alone applications as distributed applications.
2. Description of Related Art
Recently, ISDN services provided by public phone companies are becoming available world-wide. It is now cost-effective to utilize these services in place of modems to support applications that require high-speed data exchange among personal computers. Distributed applications (for example, a computer teleconferencing system, on a remote desktop presentation system) are good examples of applications using the ISDN technology.
In such distributed applications, the most important feature is to display in real time the same information on the screen or in windows of personal computers connected by a network. Displaying an identical screen or windows on interconnected personal computers in a distributed system is called "screen sharing" or "window sharing".
The effectiveness of using ISDN services in real-time applications for supporting screen sharing depends on how the bandwidth of ISDN channels is utilized. For instance, the 64 kilo bit-per-second (kbps) of the ISDN B channel is relatively high for text-based screen sharing between personal computers. However, it is not good enough to allow graphics or image-based screens to be displayed locally and remotely in real time. For example, to transmit data on a screen having 640.times.480 resolution and 16 colors (4-bits per pixel), we need about 1200 kbps (640*480*4) of bandwidth are needed for the transmission. Therefore, sending screen data between personal computers is not an appropriate method to support the screen sharing or window sharing in real time.
Another method for supporting screen sharing is to build the screen sharing as a special feature into each distributed application which is difficult to develop. The reason is that, in each distributed application, it involves a lot of efforts to define and to support a protocol (or conversation) between application modules on each personal computer, and to install all application modules on each personal computer which will waste memory and CPU resources on doing the redundant processing.
While the following description is mainly made with regard to personal computers, the present invention can be applied to other sizes of computers.
Relevant patent publications are Japanese Published Unexamined Patent Application (JPUPA) 60-128769, JPUPA 62-150960, and JPUPA 2-2794. In the techniques disclosed in those publications, for achieving a remote conference system wherein the same screen is displayed at remote terminals, image or graphics information transferred in advance and stored at every remote terminal. However, in these techniques, control (program) for the remote conference system is actually performed at each terminal (note that as described later according to the present invention a program is executed only at one terminal, or processor). Further in these techniques, a special design for communicating control data among the terminals and achieving the screen sharing is needed, and therefore the configuration becomes complicated.